Currently marketed switches and cross-connects are non-blocking. Examples include Alcatel's 1100 (HSS and LSS), 1641 and 1644 switches, AT&T's II and DACS III switches (Lucent technology), TITAN's 5300 and RN64 series, Siemens EWSXpress 35190 ATM Core Switch and Switching Faulty CC155 systems, Newbridge's 3600, 3645, 36150 and 36170 MainStreet switches and the Stinger family of ATM switches.
A review of ATM (asynchronous transfer mode) switching products, namely "The ATM Report", Broadband Publishing Corporation, ISSN 10720981X, 1996 surveys 10 switches of which nine are completely non-blocking and one, CISCO, has a positive but very low blocking probability (3% probability of blocking at 2 Gbps).
The ITU-T Recommendation G.782 (International Telecommunication Union, Telecommunication Standardization Sector, 01/94) includes Section 4.5 entitled "Blocking" which states:
"The existence of cross-connections in a cross-connect equipment can prevent the set-up of a new cross-connection. The blocking factor of a cross-connect is the probability that a particular connection request cannot be met, normally expressed as a decimal fraction of 1. Fully non-blocking (i.e. blocking factor=0) cross-connects can be built. Some simplification in design, and hence cost, can be realized if a finite blocking factor is acceptable. It is not the invention of this Recommendation to specify target blocking factors for individual cross-connect equipment. The impact of non-zero blocking factor on network performance is dependent on network design and planning rules.
"There is a class of cross-connect matrices known as conditionally non-blocking in which there is a finite probability that a connection request may be blocked. In such cross-connects, it is possible, by re-arranging existing connections, to make a cross-connection which would otherwise be blocked. As an objective, in such cases, rearrangements should be made without interruption to rearranged paths.
"It may be necessary in a nominally non-blocking, or conditionally non-blocking cross-connect, to accept some blocking penalty associated with extensive use of broadcast connections. This is for further study."
A later document "ATM functionality in SONET digital cross-connect systems--generic criteria", Generic Requirements CR-2891-CORE, Issue Aug. 1, 1995, Bellcore (Bell Communications Research) states as a requirement that "A SONET DCS with ATM functionality must meet all existing DCS requirements from TR-NWT-000233". The TR-NWT-000233 publication (Bellcore, Issue Nov. 3, 1993, entitled "Wideband and broadband digital cross-connect systems generic criteria") stipulates the following requirement (R) 4-37:
"For a two-point unidirectional cross-connection, non-blocking cross-connection shall be provided. Non-blocking means that a cross-connection can be made regardless of other existing connections. Rearranging the existing cross-connections to accommodate a new cross-connection is acceptable only if the rearrangement is performed without causing any bit error for the rearranged cross-connections."
The disclosures of all publications mentioned in the specification and of the publications cited therein are hereby incorporated by reference.